1. Field of the Invention
The present invention relates to a liquid crystal display device suitable for use in, for example, a portable information terminal, a personal computer and the like and a manufacturing method for the liquid crystal display device, and more particularly, it relates to a liquid crystal display device at least one of whose substrates is made of plastic and a manufacturing method for the liquid crystal display device.
2. Description of the Related Art
In most conventional liquid crystal display devices, glass substrates are used for sandwiching a liquid crystal layer. This is because the glass substrate is inexpensive and has very stable reliability against gasses such as oxygen and liquids such as water used in the manufacturing process. In addition, the glass substrate exhibits sufficient heat resistance even when an active element such as a TFT (thin film transistor) and an MIM (metal insulator metal) transistor is formed on the substrate, it has excellent smoothness on its surface, and can be used in large dimensions. The glass substrate is, however, heavy and brittle, and disadvantageously loses its smoothness when it is manufactured in a small thickness.
Accordingly, a plastic substrate and a film substrate, which are light, difficult to break and are applicable to a thin liquid crystal display device, are recently in the spotlight. Such a substrate is now used merely in a small liquid crystal display device for a pocket calculator or the like, and is characterized by having a surface more easily processed than the surface of a glass substrate.
Moreover, various techniques have recently been proposed for making thinner a liquid crystal display device and decreasing the manufacturing cost by unifying its composing members. For example, Japanese Laid-Open Patent Publication No. 5-264982 describes a technique of forming irregularities on the substrate surface by an embossing process so as to use a convex portion as a spacer. Also, Japanese Laid-Open Patent Publication No. 56-95217 describes a technique of forming irregularities on the substrate surface facing a liquid crystal layer by etching so as to use a convex portion as a spacer. Such techniques are advantageous in forming the spacer and the substrate as one member.
Furthermore, Japanese Laid-Open Patent Publication No. 5-264982 discloses a liquid crystal display device having a shock-resistant structure. In the shock-resistant structure, stripe-shaped protruding spacers are formed as a part of one of a pair of substrates and the stripe-shaped spacers are attached to the other substrate through an adhesive. In addition, Japanese Laid-Open Patent Publication No. 7-28071 discloses a wall structure, which is similar to the above-mentioned shock-resistant structure, for improving a shock resistance of a ferroelectric liquid crystal display device. This wall-structure is formed on a substrate by using a photosensitive resin, such as a resist material, and is formed in a stripe shape. In addition, Japanese Laid-Open Patent Publication No. 6-301015, which is assigned to the same assignee of the present application, discloses a liquid crystal display device in which a fine pixel is surrounded by a polymer wall.
Furthermore, Japanese Laid-Open Patent Publication No. 58-219526 discloses a substrate integrated with a polarizing plate and a reflection plate. Japanese Laid-Open Patent Publication No. 3-289622 describes a technique of forming irregularities on a substrate surface and also forming a metallic film on the irregular surface. These techniques are advantageous in forming the reflection plate and the substrate as one member. As a general method of producing a reflection plate, the surface of a plate is made irregular by a variety of methods such as etching, embossing and thermal sagging, and then a metallic film is formed on the irregular surface.
Conventionally, the reflection plate and the like are generally adhered to a desired substrate by using an adhesive agent or the like. The spacer is conventionally sprayed in general, but a technique of integrating a spacer with a plastic substrate has recently been proposed.
However, the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication Nos. 5-264982 and No. 7-28071 suffers from the following problems. A liquid crystal material partitioned by the stripe-shaped structure tends to move along the longitudinal direction of the stripe shaped structure by an external pressure applied to the liquid crystal display device, resulting in deterioration of display quality. This problem is severe in the case where a relatively thin substrate or a substrate formed of a plastic plate is used.
A plastic substrate is, however, several times as expensive as a glass substrate, and hence it is very difficult to replace the glass substrate at present. For the replacement, not only the cost of the substrate itself must be decreased but also the entire manufacturing cost for a liquid crystal display device must be decreased and/or the manufacturing process for the liquid crystal display device must be simplified.